Method of refining lead



July 27, 1937. P. w, DAVIS I METHOD OF REFINING LEAD Filed Sept. 9, 1933 Patented July 27, 1937 UNITED STATES PATENT OFFICE Claims.

" these ends, the present invention consists of the.

method and apparatus hereinafter described and particularly defined in the claims.

In the accompanying drawing, Fig. 1 is a diagrammatic view of the preferred form of apparatus for practising the present invention; Fig. 2 is a section on line-22 of Fig. 1; Fig. 3 is a section on line 33 of Fig. 1; and Fig. 4 is a sectional elevation of the oxide trough or launder.

The illustrated embodiment of the invention comprises-a melting furnace 6 which may be of the type described in mysecond patent above referred to. Scrap storage battery plates con- 25 sisting of lead-antimony alloy, litharge, and possibly other salts and oxides of lead, together with any pieces of wood and rubber that cost too much a by furthering the absorption of antimony by the oxide. In order to promote additional contact, the stream of molten alloy and oxide is run into a chute 8, preferably of stepped formation, as described in said patent. In tumbling or rolling down the chute, the molten alloy and molten litharge in the stream are thoroughly intermixed. The molten materials, are discharged into a forehearth it, in which the lead settles in a quiet pool with the oxide floating on top. The lead which has been reduced to substantial- 1y any desired degree of softness, is withdrawn by means of a siphon tap into a kettle 9?.

Scrap is preferably charged into the melting furnace at such intervals that molten lead and litharge flow continuously to the forehearth.

"Ihe oxide which floats on the metal in the forehearth comprises melted litharge which has taken up antimony, possibly with other lead salts, as well as other impurities in the form of sulphur and iron compounds, and silica and magnesia. This material is then conveyed into a smelting furnace for reduction to metal. The smelting operation may 'be carried out as a batch process and inasmuch as material is being more or less continuously fed into the forehearth from the melting furnace, two smelting furnaces are employed, these being indicated generally at M and I6. One of the smelting furnaces is supplied with a charge of oxide to a definite level. While this charge is being reduced, the stream of oxide is fed into the other furnace. Since both furnaces are of the same construction, it will be sufiicient to describe one only. ,A chute or passage l8 leads from the forehearth to the smelting furnace M which is heated by a burner indicated diagrammatically at 20. A measured amount of reducing material, preferably in the form of hard coal screenings, is added and allowed to react with the melted oxide until the action is completed, or nearly so. The metal alloy reduced from the antimonial litharge is withdrawn by a siphon tap into a kettle 2t. The composition of the metal withdrawn at N may be controlled by the amount of reducing agent added to the batch. If a sufflcient amount of reducing agent for complete smelting is used, and a suficient temperature maintained, all of the metals contained in the oxide will find their way into the final product with the exception of such antimony as may be volatilized. In the absence ofvolatilization of antimony, the final alloy 3 obtained from ordinarybattery .plates would be in proportion of about 93% lead and 7% antimony. There will remain a slag-like residue comprising any unreduced oxides and any sulphate and impurities derived from the original battery plates.

By using less than enough reducing agent for complete smelting, antimony will be held back in the unreduced oxide, and a softer lead obtained at 26. When the reducing agent is thus limited in quantity, the result is the same as if it acted with greater effect upon the leadthan upon the antimony present. infect the lead may be carried to a softness of less than 1% antimony. It

' on the pool of metal in the furnace.

The residue remaining after incomplete reduction in the furnace I4, is then passed to a furnace 26 in which complete reduction takes place. In order to convey the residue from the furnace l4 to the furnace 26, a transfer throat or passage 28 is provided, access to this throat being normally closed by two doors 30 and 32. The doors are opened and the residue is raked toward the throat 28 by a rabble inserted through the door 32, and is pushed by means of another rabble inserted through the door 30 into the final furnace 26. This furnace 26 is of a construction similar to the furnace l4, except that it is designed to operate at a higher temperature for complete reduction of any refractory oxides and sulphates that may exist. in the original charge. The alloy product is withdrawn by a siphon tap at 34 and the ultimate residue is raked out of the furnace outlet 36. The alloy obtained at 34 depends upon the proportions of lead and oxide in the residue and these proportions in turn depend upon the extent of smelting in the furnace l4. Ordinarily there will be used in the furnace l4 about of the amount of reducing agent required for complete smelting, in which case the alloy 24 is a moderately hard lead containing from 1 to 2% antimony, and the alloy obtained at 34 consists of a small quantity of material containing about equal parts of lead and antimony. The ultimate residue withdrawn at 36 is commercially of small or no value.

The process of smelting in two stages offers the important advantage that the primary reduction in the first furnace may be carried out at a relatively low temperature (about 1800 F.) while the higher temperatures for reducing refractory compounds in the final furnace need to.

be applied to only a small body of material.

It will be understood thatv the showing of furnaces is diagrammatic only, and that the final furnace 26 may be a blast furnace if any highly refractory compounds are present or if it proves commercially desirable.

According to a modified procedure, the twin furnaces l4 and, I6 which have been described above as necessary for the sake of keeping up with the continuous flow of oxide, are not employed. A single furnace I4 of larger capacity and greater length is then used, and the oxide is permitted to accumulate in the forehearth during the time that smelting is taking place in the furnace M. The residue resulting from the incomplete smelting is handled in the final furnace 26, as in the method above described.

According to another method employing only one smelting unit, the oxide is not held back in the forehearth, but flows continuously into the single smelting furnace M. A fine crushed reducing agent is continuously supplied at a controlled rate near the entrance of the oxide by a mechanical feeder indicated generally at 22. The

oxide and reducing agent together flow slowly on the surface of the metal bath in the metal furnace. The oxide is reduced as it flows until upon reaching the farther end, the reduction iscompleted to an extent determined by the proportions of original charge in the melting furnace.

reducing agent introduced;

The present invention also contemplates a process whereby the moderately hard lead obtained at 24 is further refined. To this end, this material is returned for introduction into the Inasmuch as the original scrap contains a sufficient amount of litharge. to take up a considerably -melting furnace.

plates, the additional antimony introduced by returning the relatively hard lead is readily taken care of. In order that adequate contact between the alloy and the litharge may be promoted, the alloy, while still molten, is poured over the charge of battery plates when they are placed in the The molten alloy breaks into small streams and penetrates the mass of material, thereby assuring contact between streamlets of the molten alloy and the litharge as the melting of the charge progresses. Alternatively, the contents of the kettle 24 may be dumped while still molten on a pile of battery plates which are awaiting treatment In any case, the object of the method. is to divide the alloy to be refined into small drops or streams which are ready for immediate and intimate contact with the litharge in the'melting furnace and in the chute 8. If this method is practised, only two ultimate metal products are obtained, namely, a soft lead which may contain as little as .002% antimony recovered at l2, and an alloy having a high percentage of antimony recovered at 34.

In addition to the process and apparatus above described, the present invention comprehends some further details which will now be described. The chute 8, which is illustrated in section in Fig.2, is constructed with a View to long life and freedom from leakage. As shown in Fig. 2, this chute comprises a lower layer of refractory basic bricks 40, side walls 42, and an arch 44. The central brick of the lowermost layer 40 is subject to erosion under the influence of the hot stream of oxide and metal. Also the oxide tends to penetrate the crevices of the bricks, eating out enlarging passages which may eventually result in allowing the stream of oxide and metal to escape from its'proper course. To obviate these difficulties, the bottom and a part of the side walls of the chute are' provided with water jackets, indicated at 46 and 48 respectively,

through which water may be continuously circulated. It may, in fact, be unnec'essary to provide for continuous circulation of the water if the temperature is kept down by permitting a small quantity to vaporize, sufficient fresh water being supplied to make up for vaporization. It will be observed that any oxide flowing through the crevices between the bricks will eventually harden or freeze as it nears the cooled area protected by the water jacket. As a consequence, this'frozen oxide will effectively seal the crevices and prevent any further action. Furthermore, the central brick 40 will start to wear down until it reaches a point at which its surface is cool enough to cause freezing of a thin layer of oxide thereon, after which no further erosion takes place. .In other words, the brick eventually assumes a thickness at which equilibrium conditions are established wherein a refractory film of oxide is maintained hardened on account of the cooling effect from below while the main stream of oxide and metal flows constantly over it.

The chutes or launders I8 for conveying the antimonial litharge from the forehearth to the smelting furnaces are also water-backed, the

construction being indicated in Fig. 3. The oxgreater amount of antimony than exists in the metal from the stream of hot oxide. This film is illustrated in exaggerated form by the hatching in Fig. 3.

It is important that the rapid flow of oxide on the surface should not be impeded or obstructed in such a way as to cause 'oxide to drop or fall on the chute. Immunity from corrosion depends on the formation of a thin film of frozen oxide over which the molten oxide glides free from actual contact with the metal of the launder. The presence of any small irregularity or obstruction, which would cause the oxide to fall by even a small fraction of an inch, would, result in breaking of the frozen oxide film, so that the oxide would impinge on the metal surface and slowly eat through the wall in spite of the water behind it.

In operation, when twin furnaces are employed, one of the troughs I8 is closed by a piece of refractory material such as fire brick, while the other is left open to convey the oxide into the smelting furnace.

The oxide from the forehearth, instead of being smelted, may be treated directly. To this end, the forehearth has aside chute 52 through which the oxide may be passed while hot and in a fine stream or streams into immediate largesurface contact with a cool fluid, illustrated as a body of water in the vessel 54. The sudden cooling of the molten material produces a disruptive contraction solidifying the oxide into fine granules which are amenable to chemical treatment, without the necessity of grinding.

As a further feature of the invention, chemical separation of sulphur may be practised in the forehearth. To this end, there is introduced into the forehearth a quantity of a weak alkali salt, such as soda ash, which reacts with lead sulphate in the oxide to form sodium sulphate. The sodium sulphate, being lighter than the oxide, floats on the stream thereof during passage through the chute l8, as illustrated in Fig. 4. The chute is provided with a closure 56 which is open at the bottom to permit the molten antimonial litharge to run through and which extends at the top above the chute. The sulphate being unable to pass along with the oxide, runs over the top and sides of the chute and. may be collected in any suitable manner. Although the removal of the sulphur in the forehearth is not necessary, it forms a desirable adjunct to the present process in that it permits reduction to metal in the smelting furnaces at a minimum temperature and with minimum handling of refractory sulphur-containing residues.

Although the invention has been described as applying principally to the recovery of lead from lead-antimony alloys, such as. exist in battery plates, it is equally applicable to the refining of any lead alloys containing any other metal or metals more easily oxidizable than lead, such as arsenic, tin, antimony and copper. The refining action in any case depends on the fact that the lead oxide gives. up its oxygen, or at least a part of it, to the alloy metal which has va greater afiinity for oxygen than does lead.

Having thus described the invention, what is claimed is:

1. The method of refining a lead alloy containing one or more metals more easily oxidizable than lead, such as arsenic, antimony, tin or copper, which consists in continuously melting the alloy, contacting the molten alloy with lead oxide to refine the lead, continuously collecting the molten'lead and oxide in a pool, separating the oxide from the lead, continuously running the separated oxide to one or the other of a pair of smelting furnaces, and smelting the oxide with reducing agent by a batch process in one of said furnaces while running oxide into the other.

2. The method of refining scrap lead, such as scrap storage battery plates and the like, containing lead-antimony alloy and lead oxide which consists in melting the scrap, the oxide contacting with the metal and taking up antimony therefrom to cause refinement of the lead, permitting the refined lead to settle in a pool, continuously separating antimonial oxide from the lead, continuously running the separated oxide to one or the other of a pair of smelting furnaces, and smelting the oxide with reducing agent by a batch process in one of said smelting furnaces while running oxide into the other.

3. The method of treating antimonial litharge which consists in heating the litharge in the presence of insufiicient reducing agent to reduce the litharge completely, thereby forming a leadantimony alloy and a residue floating thereon, said residue consisting of lead and antimony compounds rich in antimony, separating the residue from the molten alloy, and thereafter heating the residue to a higher temperature in the presence of suflicient reducing agent for complete reduction to obtain an alloy high in antimony content.

4. The method of refining scrap lead, such as scrap storage battery plates and the. like containing lead, antimony and oxide which consists in melting the mixture of metal and oxide whereby the oxide takes up antimony, separating the antimonial oxide. from the lead, incompletely reducing the oxide to obtain a relatively hard lead, and mixing the hard lead with scrap about to be subjected to the melting operation, whereby the hard lead may be refined in conjunction with the scrap.

5. The method of refining scrap lead, such as scrap storage battery plates and the like containing lead, antimony and oxide which consists in melting the mixture of metal and oxide whereby the oxide takes up antimony, separating the antimonial oxide from the lead, incompletely reducing the oxide to obtain a relatively hard lead, and pouring the molten hard lead in small streams over scrap in the furnace and about to be subjected to the melting operation, whereby it becomes intimately mixed with the oxide in said scrap.

PHILIP W. DAVIS. 

